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Rev. 1 del 24.10.2017
ACTION PRINCIPLES
Muscular electrostimulation
Electrostimulation is a technique that, by means of electric pulses that act on the
muscle's motor points (motoneuron), causes muscular contraction responses similar
to voluntary contractions.
Most of human body muscles belong to the striated or voluntary muscle category,
with approximately 200 muscles on each side of the body (about 400 in all).
The physiology of muscular contraction
The skeletal muscle performs its functions through the contraction mechanism.
When a person decides to make a movement, the motor center of the brain sends
an electric signal to the muscle that is to contract.
When the electric signal reaches the muscle, the motor plaque of the muscle
surface produces the depolarization of the muscle membrane and the release of
CA++ ions inside it. The Ca++ ions, interacting with the actin and myosin molecules,
activate the contraction mechanism which leads to the shortening of the muscle.
The amount of energy needed for the contraction is provided by the adenosine
triphosphate (ATP) and is supported by an energy recharging system based on
aerobic and anaerobic energy mechanisms which use carbohydrates and fats. In
other words, electric stimulation is not a direct source of energy but it works as a tool
that causes a muscular contraction.
The same type of mechanism is activated when the muscular contraction is
produced by the EMS; they have the same function of a pulse naturally transmitted
by the motor nervous system. When the contraction is over, the muscle relaxes and
returns to its original state.
Isotonic and isometric contraction
An isotonic contraction occurs when, during a movement, the interested muscles
exceed outside resistance by shortening, thus provoking a constant state of tension
in the ends of the tendons. When outside resistance impedes its movement, the
muscular contraction, instead of provoking a shortening effect, causes an increase
in the tension at the extremes; this is called isometric contraction. In the case of
electrostimulation, a stimulation for isometric conditions is normally used because it
permits a more powerful and efficient contraction.
The distribution of different types of fibers in the muscle
The relation between the two main categories (type I and type II) can vary
noticeably.
There are muscular groups that are typically made up of type I fibers, like the soleus,
and muscles which are made up of only type II fibers, like the orbicular muscle, but
the majority of the human body muscles are composed of a combination of the
two types. Studies on the distribution of fibers in the muscle mass have highlighted